An inkjet printing system typically includes one or more printheads and their corresponding ink supplies. Each printhead includes an ink inlet that is connected to its ink supply and an array of drop ejectors, each ejector including an ink pressurization chamber, an ejecting actuator and an orifice through which droplets of ink are ejected. The ejecting actuator can be one of various types, including a heater that vaporizes some of the ink in the pressurization chamber in order to propel a droplet out of the orifice, or a piezoelectric device which changes the wall geometry of the chamber in order to produce a pressure wave that ejects a droplet. The droplets are typically directed toward paper or other recording medium (sometimes generically referred to as paper herein) in order to produce an image according to image data that is converted into electronic firing pulses for the drop ejectors as the print medium is moved relative to the printhead.
Motion of the print medium relative to the printhead can be accomplished by keeping the printhead stationary and advancing the print medium past the printhead while the drops are ejected. This architecture is appropriate if the nozzle array on the printhead can address the entire region of interest across the width of the print medium. Such printheads are sometimes called page-width printheads.
A second type of printer architecture is the carriage printer, where the printhead nozzle array is somewhat smaller than the extent of the region of interest for printing on the print medium and the printhead is mounted on a carriage. In a carriage printer, the print medium is advanced a given distance along a print medium advance direction and then stopped. While the print medium is stopped, the printhead carriage is moved in a direction that is substantially perpendicular to the print medium advance direction as the drops are ejected from the nozzles. After the carriage has printed a swath of the image while traversing the print medium, the print medium is advanced; the carriage direction of motion is reversed; and the image is formed swath by swath.
Inkjet ink includes a variety of volatile and nonvolatile components including pigments or dyes, humectants, image durability enhancers, and carriers or solvents. A key consideration in ink formulation is the ability to produce high quality images on the print medium. During periods when ink is not being ejected from an ejector, the ink viscosity at the nozzle can change. For example, the volatile components of the ink can evaporate through the nozzle. Such changes can make the drop ejection process non-uniform, so that the image quality can be degraded. In addition, dust, dried ink or other particulates can partially block a nozzle or make the wettability of the nozzle face around the nozzle non-uniform so that ejected drops can be misdirected from their intended flight paths. Additionally, when an ink supply is changed over, for example when an ink tank is replaced, some of the volatile ink components can evaporate at the point of the connection of the ink supply and cause an intake of air into the ink supply passageways.
In order to maintain the drop ejecting quality of the printhead so that high quality images are produced even after periods where one or more nozzles has been inactive, a variety of maintenance actions have been developed and are well known in the art. These maintenance actions can include capping the printhead nozzle face region during periods of nonprinting, wiping the nozzle face, periodically spitting drops from the nozzles into the cap or other reservoir that is outside the printing region, and priming the nozzles by applying a suction pressure at the nozzle face. To remove air accumulated in the ink supply passageways, suction priming by a vacuum applied at the nozzle face of the printhead is typically used. However, suction priming tends to remove a significant amount of ink from the printhead. This means that less ink is available for printing, and also that more waste ink should be stored in the printer.
What is needed is a way to select a level of maintenance after an ink supply changeover that is more efficient in ink usage. More efficient ink usage makes it possible for the user to change ink supplies less frequently, saving the user both effort and money, and also putting less waste into the environment.